1. Technical Field
This invention relates to the field of fermentation processes. More particularly, it relates to methods and means for controlling bacteria in fermentation processes for producing ethanol.
2. Background of the Art
A commonly-employed method of producing ethanol involves fermentation based on yeast. This process consists basically of the following operations: (a) molasses handling, dilution, clarification and heat treatment, (b) anaerobic fermentation by a selected yeast strain, previously grown under controlled conditions, (c) yeast separation from the broth, and (d) alcohol separation by distillation and eventual storage. For detailed descriptions and technical details, see, for example: Harrison, J. S. and Graham, J. C. J., “Yeast in Distillery Practice” in A. H. Rose and J. S. Harrison (Eds.) “The Yeasts” 3 (6) 283-348 (1970), Academic Press; Kampen, W. H., Sugar y Azucar 70 (8) 36-39, 42-43 (1975); and L'Anson, J. A. P., Process Biochem. 11 (7) 35-39 (1971). Many processing operations begin with the juice or syrup which has been extracted from a solid fiber matrix of a sugar source selected from, for example, sugar cane, corn, or sugar beets, while others begin with direct fermentation of the sugar source which has been comminuted into fragments or highly pulverized. Such methods represent generally efficient ways to produce a variety of alcohols, and in particular ethanol, from a selected fermentation substrate.
However, a problem is encountered when bacteria contaminate the fermentation substrate. The bacteria, when present at relatively high levels, compete with the yeast and may reduce the fermentative yield. Furthermore, the bacteria may cause flocculation, requiring additional measures to obtain ethanol therefrom. Those skilled in the art have developed various means of addressing the bacteria problem. The most commonly used method at present involves adding biocides to the substrate. Examples of these biocides include quaternary ammonium compounds, carbamates, and halogenated phenols. Alternatively or in combination with biocides, hydrogen peroxide may be used or antibiotics may be used. Such may include, for example, an antibiotic known as KAMORAN HJ™, which is defined as 4-[2-[5-ethyl-5-[5-[6-hydroxy-6-(hydroxymethyl)-3,5-dimethyl-oxan-2-y]-3-methyl-oxolan-2-yl]oxolan-2-yl]-9-hydroxy-2,8-dimethyl-1,6-dioxaspiro-[4.5]dec-7-yl]-3-methoxy-2-methyl-pentanoate.
Unfortunately, some biocides and antibiotics may undesirably contaminate the ethanol, cause flocculation, or generally require a post-treatment or additional processing of the fermentation medium and/or the alcohol product. Such post-treatments or additional processing may add to the time, cost, and/or convenience of producing the ethanol. Biocides and antibiotics may also reduce yeast level during the process, which is undesirable.
In view of the above, it would be desirable in the art to find methods and means for preparing ethanol via fermentation processes that eliminate or reduce these problems and/or the need for biocides and antibiotics conventionally used for such processes.